In the production of many semiconductor components, the handling of a wafer represents an important factor for a successful production process. The production of chip cards and thin integrated circuits, for example, necessitates that very thin wafers are handled, which have to be transported and held without the risk of breaking.
Many semiconductor processes, such as the production of circuit elements for power electronics, additionally require back-surface processes, which comprise a deposition of solder or alloy layers on the back of the fully processed circuit wafer; in a subsequent alloying or sintering step of these layers, high temperatures occur, which may exceed 400° C. The wafer holding device must then guarantee perfect functioning in the case of these ambient temperatures.
A known method of handling thin wafers is so conceived that the front face of the wafer is provided with a protective foil, which is typically a polymer foil. The wafer is held by the carrier foil during the thinning sequence. The possibility of using this known method comprises wafers having a diameter of 6 inches and a thickness which must not exceed 100 μm. Handling and transport of wafers having a thickness of less than 100 μm is prevented by the fact that the wafers will bend, whereby the risk of breaking increases significantly for the thin wafers. It follows that the method does not offer any possibility of handling extremely thin wafers with comparatively large diameters.
Another method makes use of a carrier wafer to which the wafer to be thinned is reversibly attached by means of an adhesive film which is adherent on both sides, e.g. a thermally strippable film. The thermally strippable film can be stripped by subjecting it to a certain temperature. The method is adapted to be used for wafers having a thickness of not less than 20 μm, and also wafers having a large diameter can be held safely. The method is, however, disadvantageous insofar as, due to the adhesive film used, which is typically a polymer film, the method is not suitable for back-surface processes involving temperatures above 130° C.
Furthermore, electrostatic holding devices, so-called electrostatic chucks, are known for taking up wafers by means of electrostatically generated holding forces and for holding these wafers during a production process. The holding force can be generated by means of a monopolar electrode or by means of bipolar electrodes. In the case of a monopolar electrode, the wafer to be held serves as a counterelectrode and must therefore be connected to ground; during a dry etching process, for example, this connection to ground is obtained by the conductive etch plasma.
The known electrostatic holding devices are, however, disadvantageous insofar as they have a solid structural design and are, typically, fixedly installed in a processing chamber. In addition, the known electrostatic holding devices are dependent on an external power supply. Hence, the known electrostatic holding devices can only be used as holding devices for holding the wafer at one location, but they cannot be used for the purpose of transport, e.g. for taking up a thinned wafer at the location where the thinning sequence has been executed and transporting it to a second location where e.g. processing of the back surface will take place.
It follows that the handling of thin wafers, which necessitate high-temperature processing steps, such as sintering or alloying, is problematic, since devices for handling such wafers are not available.
Furthermore, a support device is, at present, not available, which permits chips that have been subjected to a dicing process of the type described e.g. in DE-19962763 A1 to be taken up and detached selectively.
EP 0 552 877 A1 discloses an electrostatic chuck and a method of exciting the same. The electrostatic chuck is part of a multi-chamber system for processing integrated circuits. A wafer transport plate supports a wafer by means of an electrostatic holding device. The wafer transport plate itself is connected to a base of the multi-chamber system by a four-bar connecting joint in such a way that the wafer can be moved to and fro between various chambers by displacing and rotating the wafer support plate. The electrostatic holding device comprises a dielectric base layer having arranged thereon electrode strips which are incorporated in a dielectric encapsulating layer. The dielectric base layer is formed on the upper surface of the wafer support plate making use of conventional deposition, masking and etching steps.
EP 0 506 537 A1 discloses an electrostatic chuck comprising an integral five-layer structure, which is suitable for holding and transporting a semiconductor silicon wafer in a production process for electronic components. A particularly characteristic feature of this electrostatic chuck is that the wafer held will be released immediately when a voltage applied to electrodes of the chuck is switched off. It is the object of the present invention to provide a concept for an improved handling of wafers.